The characterizing features of the sub-combat unit described in the above-mentioned patent are that the target detector is pivotally disposed on a journal shaft which is parallel to the line of symmetry of the warhead so as to permit outward pivoting of the target detector from a closed position where the optical axis of the target detector coincides with the line of symmetry of the warhead, to an opened position where the optical axis of the target detector is parallel to the line of symmetry of the warhead to permit a free view of the target detector beside the warhead. In addition, a carrier surface is pivotally disposed on a journal shaft which is also parallel to the line of symmetry of the warhead so as to permit outward pivoting of the carrier surface from a closed position to an opened position beside the warhead.
By a suitable aerodynamic design of the sub-combat unit and the retarding area of the detector and carrier surface, there will be obtained a suitable fall velocity of the sub-combat unit and further an impelling moment about the spinning axis which gives the sub-combat unit its rotation. This is achieved without the aid of a parachute, which is an advantage since the parachute is bulky and requires space. Therefore, more space in a carrier shell can instead be made available for the warhead proper.
Even thought the above-described sub-combat unit has proved to possess superior properties with respect to fall velocity and scanning rotation, it has been desired in the art to increase the retarding area even further. This may, for instance, be the case when it is desired to employ heavier warheads. The retarding area of the target detector and carrier surface is restricted to the cross-sectional area of the cylindrical sub-combat unit body, which may entail that the fall velocity will become too high with the existing size of the retarding area if, at the same time, the weight of the warhead is increased.
Swedish patent application number 8903474-8 corresponding to U.S. Pat. No. 5,088,414 describes a sub-combat unit in which the retarding area has been made considerably larger. The characterizing feature of the sub-combat unit is that two diametrically located carrier surfaces are pivotally disposed each on its own shaft located in a plane which is at right angles to the axis of symmetry of the warhead, and pivotable from a closed position where the carrier surfaces follow the casing surface of the sub-combat unit, to a 90.degree. opened position where both of the carrier surfaces form a retarding area for the fall velocity of the sub-combat unit.
In this case, the carrier surfaces are made of an elastically flexible material, so that, when they pivot out from their closed position, they are at the same time bent to a substantially straight or gently curved surface.
The advantage inherent in the above-described design, in addition to the larger retarding area, is that both of the carrier surfaces may be made comparatively thin, which is favorable from the point of view of weight and payload. For example, the carrier surfaces may be made of titanium and bent so that, in their opened position, they have a certain radius. The bending may be varied and the carrier surfaces may be of different lengths, in which event further parameters for varying the aeronautical properties of the unit will be obtained.
Even if the two carrier surfaces are designed with an accurately specified geometry in accordance with known ballistical laws, it may occur at certain angles of wind impingement in relation to the carrier surface that the momentaneous is disturbed, so that a disturbance (unwanted pendulum motion, instability) occurs in the sub-combat unit to the detriment of the scanning movement.